On Mon, May 29, 2023 at 3:39 AM Adam Goldman <[email protected]> wrote:
> This patch makes udhcpd respond correctly to queries from BOOTP clients.
>
> It contains the following changes:
>
> The end field, or DHCP_END option, is required in DHCP requests but
> optional in BOOTP requests. Only complain about missing end fields if
> there are DHCP options in the packet. However, we still send an end
> field in all replies, because some BOOTP clients expect one in replies
> even if they didn't send one in the request.
>
> Requests without a DHCP_MESSAGE_TYPE are recognized as BOOTP requests
> and handled appropriately, instead of being discarded. We still require
> an RFC 1048 options field, but we allow it to be empty.
>
> Since a BOOTP client will keep using the assigned IP forever, we only
> send a BOOTP reply if a static lease exists for that client.
>
> BOOTP replies shouldn't contain DHCP_* options, so we omit them if there
> was no DHCP_MESSAGE_TYPE in the request. Options other than DHCP_*
> options are still sent.
>
> The options field of a BOOTP reply must be exactly 64 bytes. If we
> construct a reply with more than 64 bytes of options, we give up and log
> an error instead of sending it. udhcp_send_raw_packet already pads the
> options field to 64 bytes if it is too short.
>
> This implementation has been tested against an HP PA-RISC client.
>
>
> --- networking/udhcp/common.c.orig 2023-05-22 18:41:39.000000000 -0700
> +++ networking/udhcp/common.c 2023-05-21 19:18:15.000000000 -0700
> @@ -234,6 +234,7 @@
> void FAST_FUNC init_scan_state(struct dhcp_packet *packet, struct
> dhcp_scan_state *scan_state)
> {
> scan_state->overload = 0;
> + scan_state->is_dhcp = 0;
> scan_state->rem = sizeof(packet->options);
> scan_state->optionptr = packet->options;
> }
> @@ -251,12 +252,17 @@
>
> /* option bytes: [code][len][data1][data2]..[dataLEN] */
> while (1) {
> + if (scan_state->rem == 0 && !scan_state->is_dhcp)
> + break; /* BOOTP packet without end field */
> if (scan_state->rem <= 0) {
> complain:
> bb_simple_error_msg("bad packet, malformed option
> field");
> return NULL;
> }
>
> + if (scan_state->optionptr[OPT_CODE] >= DHCP_REQUESTED_IP &&
> scan_state->optionptr[OPT_CODE] <= DHCP_CLIENT_ID)
> + scan_state->is_dhcp = 1;
> +
scan_state->is_dhcp is not particularly useful.
I'm dropping it.
> +++ networking/udhcp/packet.c 2023-05-23 00:22:45.000000000 -0700
> @@ -18,6 +18,7 @@
> memset(packet, 0, sizeof(*packet));
> packet->op = BOOTREQUEST; /* if client to a server */
> switch (type) {
> + case 0:
A symbolic name is better here.
> - init_packet(&packet, oldpacket, DHCPOFFER);
> + if (!udhcp_get_option(oldpacket, DHCP_MESSAGE_TYPE))
> + message_type = 0;
> + init_packet(&packet, oldpacket, message_type);
>
> /* If it is a static lease, use its IP */
> packet.yiaddr = static_lease_nip;
> @@ -785,8 +789,13 @@
> }
>
> lease_time_sec = select_lease_time(oldpacket);
> - udhcp_add_simple_option(&packet, DHCP_LEASE_TIME,
> htonl(lease_time_sec));
> + if (udhcp_get_option(oldpacket, DHCP_MESSAGE_TYPE))
> + udhcp_add_simple_option(&packet, DHCP_LEASE_TIME,
> htonl(lease_time_sec));
> add_server_options(&packet);
> + if (!udhcp_get_option(oldpacket, DHCP_MESSAGE_TYPE) &&
> udhcp_end_option(packet.options) > 63) {
> + bb_simple_error_msg("BOOTP BOOTREPLY would be too large, not
> sending");
> + return;
> + }
Let's just pass the known result of udhcp_get_option(DHCP_MESSAGE_TYPE)
down to here, rather than calling it three times.
Applied with some changes.
Thank you.
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